This squeeze sensor can be made by knitting or crocheting a ball including resistive yarn. The ball can then be stuffed with different materials to achieve different kinds of squishiness. The ball can also be hand or machine felted, giving the surface a more uniform appearance.

Crochet

This example was crochet from regular pink yarn and stuffed with a spool-knit tube of Nm3/10 conductive yarn. Either end of the spool knit conductive yarn protrudes out from the crochet ball at opposite ends.

How to crochet a ball >> http://www.instructables.com/id/How-to-crochet-a-ball-or-a-hackey-sack/?ALLSTEPS
How to felt a knitted piece in the washing machine >> http://www.instructables.com/id/How-to-felt-a-knitted-piece/
How to felt scraps with dish washing soap in the sink >> http://www.instructables.com/id/Felt-Balls-from-Scrap-Yarn/

Knit

In the following versions of the above, the non-conductive ball is knit on a circular knitting machine, rather than crochet.

In this version a non conductive circular knit tube is stuffed with a spool-knit tube of Nm3/10 conductive and regular non-conductive yarn.

In this version the Nm3/10 conductive yarn is knit on a circular knitting machine alongside a regular white yarn. the tube is then stuffed with non-conductive stuffing and pulled tight at either end.

Felted Pompom

The felted pompom pressure sensor could also be called a squeeze sensor:
>> http://www.kobakant.at/DIY/?p=2395